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Fusarium Stub Dieback of Carnation. Paul E. Nelson, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Barbara W. Pennypacker(2), T. A. Toussoun(3), and R. K. Horst(4). (2)(3)Research Assistant, and Adjunct Professor, respectively, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; (4)Associate Professor, Department of Plant Pathology, Cornell University, Ithaca, New York 14853. Phytopathology 65:575-581. Accepted for publication 16 December 1974. DOI: 10.1094/Phyto-65-575.

The stub dieback phase of Fusarium stem rot of carnation frequently occurs in the northeastern United States. Damage on mature flowering plants consists of dieback of cut flower stubs and subsequent girdling of main branches. Fusarium roseum ‘Graminearum’ and several other Fusarium species were recovered on plates of Nash and Snyder medium exposed in greenhouses where the disease was severe. Stubs showing various degrees of dieback were collected during several months and cultured. Fusarium roseum ‘Graminearum’ and other Fusarium species were recovered from 6 to 18% of the stubs showing severe dieback, while no fusaria were recovered from those showing minimal dieback. Samples of aspen wood fibers from cooling pads, yielded F. roseum ‘Graminearum’ and other Fusarium species. Corn stalk tissue from a field adjacent to the greenhouses yielded F. roseum ‘Graminearum’. All isolates of F. roseum ‘Graminearum’ from air in the greenhouse, from carnation stubs showing dieback symptoms, from cooling pad fibers, and from corn stalks, caused a basal rot on unrooted carnation cuttings and dieback on freshly cut carnation stem stubs. Under current practices of carnation crop production, periodic outbreaks of the stub dieback disease may occur in the northeastern United States, especially during the summer months when environmental conditions favor disease development, and control of the greenhouse environment is not possible.